The invention relates to the field of polyetherimides. Polyetherimides are engineering thermoplastics that are thermally stable and find many applications under demanding elevated temperatures. Polyetherimides made by chloro-displacement methods are known.
Unfortunately, it has been discovered that chloro-substituted polyetherimides made by chloro-displacement methods exhibit diminished Relative Thermal Index properties that do not meet some commercial applications. The Relative Thermal Index is a known property that indicates how a polymer's properties degrade after being subjected to heat aging. Materials are investigated with respect to retention of certain critical properties (e.g., dielectric strength, flammability, impact strength, and tensile strength) as part of a long-term thermal-aging program conducted in accordance with Underwriters Laboratories, Inc. Standard for Polymeric Materials-Long Term Property Evaluations (UL746B). The end-of-life of a material at each test temperature in this program has been assumed to be the time when the value of the critical property has decreased to 50% of its original (as received) value.
For the foregoing reasons, there is an ongoing, unmet need for chloro-substituted polyetherimides having improved Relative Thermal Index properties, and methods of making such chloro-substituted polyetherimides.